Integrated circuit and device fabrication requires deposition of electronic materials on substrates. The deposited film may be a permanent part of the substrate or finished circuit. In this case, the film characteristics are chosen to provide the electrical, physical, or chemical properties required for circuit operation. In other cases, the film may be employed as a temporary layer that enables or simplifies device or circuit fabrication. For example, a deposited film may serve as a mask for subsequent etching processes. The etch-resistant film may be patterned such that it covers areas of the substrate are not to be removed by the etch process. A subsequent process may then remove the etch-resistant film in order to allow further processing of the substrate.
In another example of a temporary layer, a film may be employed to enhance a subsequent lithographic patterning operation. In one embodiment, a film with specific optical properties is deposited on a substrate, after which the film is coated with a photosensitive imaging film commonly referred to as photoresist. The photoresist is then patterned by exposure to light. The optical properties of the underlying deposited film are chosen to reduce reflection of the exposing light, thereby improving the resolution of the lithographic process. Such a film is commonly referred to as an anti—reflective coating (henceforth: ARC). Methods for using and fabricating vapor deposited materials with tunable optical properties are presented in U.S. Pat. No. 6,316,167.
Various physical and/or chemical deposition techniques are routinely employed for film deposition, and often more than one technique may be used to deposit a particular film. The preferred deposition method is determined by considering the desired film properties, physical and/or chemical constraints imposed by the device being fabricated, and economic factors associated with the manufacturing process. The selected process is often the one that provides an acceptable trade-off to address the pertinent technical and economic concerns.
Thermally excited chemical vapor deposition (henceforth: CVD) is a common technique used to deposit materials for integrated circuit fabrication. In a typical embodiment, a substrate is placed in a low-pressure reactor and maintained at a controlled temperature. The wafer is exposed to gaseous ambient of one or more precursors that contain the chemical elements to be incorporated in the film. The gaseous precursors are transported to the substrate surface and combine via one or more chemical reactions to form a solid film. The conditions of the reactor chamber, substrate, and precursor are typically chosen to favor chemical reactions that produce films with the desired physical, chemical, and electrical properties.
A plasma can be employed to alter or enhance the film deposition mechanism. A deposition process that employs a plasma is generally referred to as a plasma-enhanced chemical vapor deposition (henceforth: PECVD). In general, a plasma is formed in a vacuum reactor by exposing a gas mixture to an RF signal and exciting electrons to energies sufficient to sustain ionizing collisions with a supplied process gas. Moreover, the excited electrons can have energy sufficient to sustain dissociative collisions and, therefore, a specific set of gases under predetermined conditions (e.g., chamber pressure, gas flow rate, etc.) are chosen to produce a population of charged species and chemically reactive species suitable to the particular process being performed within the chamber.
Plasma excitation generally allows film-forming reactions to proceed at temperatures that are significantly lower than those typically required to produce a similar film by thermally excited CVD. In addition, plasma excitation may activate film-forming chemical reactions that are not energetically or kinetically favored in thermal CVD. The chemical and physical properties of PECVD films may thus be varied over a relatively wide range by adjusting process parameters.